Say Y or M to enable MIDI sequencer and router support. This feature allows routing and enqueueing of MIDI events. Events can be processed at a given time. Many programs require this feature, so you should enable it unless you know what you're doing.
Say Y here to enable the dummy sequencer client. This client is a simple MIDI-through client: all normal input events are redirected to the output port immediately. You don't need this unless you want to connect many MIDI devices or applications together. To compile this driver as a module, choose M here: the module will be called snd-seq-dummy.
To enable OSS mixer API emulation (/dev/mixer*), say Y here and read <file:Documentation/sound/alsa/OSS-Emulation.txt>. Many programs still use the OSS API, so say Y. To compile this driver as a module, choose M here: the module will be called snd-mixer-oss.
To enable OSS digital audio (PCM) emulation (/dev/dsp*), say Y here and read <file:Documentation/sound/alsa/OSS-Emulation.txt>. Many programs still use the OSS API, so say Y. To compile this driver as a module, choose M here: the module will be called snd-pcm-oss.
If you disable this option, the ALSA's OSS PCM API will not support conversion of channels, formats and rates. It will behave like most of new OSS/Free drivers in 2.4/2.6 kernels.
Say Y here to enable OSS sequencer emulation (both /dev/sequencer and /dev/music interfaces). Many programs still use the OSS API, so say Y. If you choose M in "Sequencer support" (SND_SEQUENCER), this will be compiled as a module. The module will be called snd-seq-oss.
Say Y here to enable HR-timer backend for ALSA timer. ALSA uses the hrtimer as a precise timing source. The ALSA sequencer code also can use this timing source. To compile this driver as a module, choose M here: the module will be called snd-hrtimer.
Say Y here to use the HR-timer backend as the default sequencer timer.
Say Y here to enable RTC timer support for ALSA. ALSA uses the RTC timer as a precise timing source and maps the RTC timer to ALSA's timer interface. The ALSA sequencer code also can use this timing source. To compile this driver as a module, choose M here: the module will be called snd-rtctimer. Note that this option is exclusive with the new RTC drivers (CONFIG_RTC_CLASS) since this requires the old API.
Say Y here to use the RTC timer as the default sequencer timer. This is strongly recommended because it ensures precise MIDI timing even when the system timer runs at less than 1000 Hz. If in doubt, say Y.
If you say Y here, the minor numbers of ALSA device files in /dev/snd/ are allocated dynamically. This allows you to have more than 8 sound cards, but requires a dynamic device file system like udev. If you are unsure about this, say N here.
Say Y here to support the obsolete ALSA PCM API (ver.0.9.0 rc3 or older).
Say Y here to include code for verbose procfs contents (provides useful information to developers when a problem occurs). On the other side, it makes the ALSA subsystem larger.
Say Y here to enable verbose log messages. These messages will help to identify source file and position containing printed messages. You don't need this unless you're debugging ALSA.
Say Y here to enable ALSA debug code.
Say Y here to enable extra-verbose debugging messages. Let me repeat: it enables EXTRA-VERBOSE DEBUGGING messages. So, say Y only if you are ready to be annoyed.
Say Y to enable the PCM ring buffer overrun/underrun debugging. It is usually not required, but if you have trouble with sound clicking when system is loaded, it may help to determine the process or driver which causes the scheduling gaps.